Chapter 21, Problem 21.63P

Interpretation Introduction

Interpretation:

A crossed Claisen reaction between methyl propionate and methyl acetate produces a mixture of products and so is not synthetically useful. The reason of the reaction between $\text{methyl 2-propionate}$ and methyl acetate, is synthetically useful, is to be explained.

Concept introduction:

In a Claisen condensation reaction, an ester with at least two $\text{α}$ protons is treated with a strong base, followed by acid workup, to produce $\text{β-}$ keto ester. In these reactions, the base deprotonates the $\text{α}$ carbon of one ester to produce an ester enolate anion, which acts as a nucleophile and attacks the carbonyl carbon of the second ester. The nucleophilic addition-elimination equilibrium favors reactants.

In a crossed Claisen condensation reaction, the enolate anion that acts as the nucleophile derives from an ester that is different from the ester it attacks.